Learning Exercise: Virtual Lab on the Visible Spectrum of Hydrogen.

This is a worksheet that makes use of the emission and absorption applets for the visible spectrum of hydrogen within the Visual Quantum Mechanics Website. It is designed to be used in a survey course for non-science majors.

Course: General Physical Science

Info

Submitted by:

Terry Bradfield

Date Last Modified:

September 05, 2001

Exercise

Virtual Lab Assignment No. 3

Virtual Lab No. 3: The Visible Spectrum of Hydrogen.

Introduction

In this lab we will see how Bohr's model of the hydrogen atom can accountfor its observed spectrum. Your goal is to find the orbit transitionsthat produce the four visible lines in the spectrum for both the emissionand absorption cases. The applets for this lab can be found at thelinks http://phys.educ.ksu.edu/vqm/html/emission.htmlfor the emission spectrum, and http://phys.educ.ksu.edu/vqm/html/absorption.html. Instructions for using the applet are included in this link. For those who don't want to calculate orbit energies themselves,
you candetermine these by using the applet located at http://home.a-city.de/walter.fendt/phe/bohrh.htm. The energy of the electron in the currently selected orbit is given inthe lower right hand corner of the applet window. Values in joulesand electron volts are given, you will need the latter unit valuefor this lab.

Procedure

The first step is to construct a table showing the electron energy in eachof its possible orbits. Although in reality there are an infinite numberof possibilities, to investigate the visible spectrum we need only considervalues from n = 2 to n = 6. The energy of the electron in each orbitcan be found either using the formula ,or by using the Bohrtheory of hydrogen applet.

Principal Quantum Number n

Electron Energy (in eV)

n = 1

n = 2

n = 3

n = 4

n = 5

n = 6

Next, load the emissionspectrum applet. This will open in a new browser window. Move the mouseover one of the spectrum lamps; when you do so,
the name of the materialin the lamp will appear next to it. Select the hydrogen lamp by clickingand dragging it to the spectrum lamp sockets. When the lamp is placed inthe socket, the visible part of the hydrogen spectrum will appear at thetop of the applet window.

Follow the instructions in the applet to add each of the energy levelsin your table to the energy level diagram in the applet. Since the graphscale is fairly coarse, you won't be able to match them exactly, but tryto get as close as you can.

With energy levels in place, you are ready to begin experimenting withtransitions. When you enter a transition in the diagram, the spectral lineto which it corresponds will appear in the section below the hydrogen spectrum,if its wavelength lies in the visible range, otherwise, nothing will happen.If you need to remove a transition, you can do so by dragging it off thegraph.

Once you have obtained all four of the visible lines in the hydrogen spectrum,complete the table below.

Spectral Line

Starting Orbit Number

Ending Orbit No.

Red

Blue

1st Violet

2nd Violet

Next,
load the absorptionspectrum applet. Add the electron energy levels to it in the same fashionas for the emission applet. Experiment with transitions until you duplicateall the absorption lines and complete the table below.

Absorption Spectrum Transition for Hydrogen

Spectral Line

Starting Orbit No.

Ending Orbit No.

1st

2nd

3rd

4th

Questions

1. Do you see any patterns in the transitions that generate the emissionspectrum of hydrogen? If so, what are they?

2. How do the transitions that generate the absorption spectrum comparewith those that generate the emission spectrum?